SPN 86566 FMI 13: Meaning and Fix
SPN 86566 FMI 13 indicates that the glow plug control module has lost its internal calibration reference, causing the ECM to report an out-of-calibration condition. This fault commonly appears after an ECU replacement or a battery disconnect event where the module’s learned offset values are erased. Technicians frequently encounter this on Deutz TCD 2.9 engines after a forced DPF regeneration, when the glow plug controller fails to re-synchronize with the ECM. The module cannot accurately command pre-heat or post-heat cycles, leading to cold-start difficulties and increased white smoke emissions.
Common Symptoms
- Hard Cold Start: Engine cranks excessively in cold ambient temperatures due to inactive or poorly timed glow plug activation.
- White Smoke: Excessive white smoke at startup and during warm-up, indicating incomplete fuel combustion from insufficient pre-heat.
- MIL Illuminated: Red or amber malfunction indicator lamp (MIL) on the dash, often accompanied by a J1939 diagnostic message.
- Reduced Power: ECM may limit engine power or torque to protect the aftertreatment system during cold operation.
Probable Causes
- ECM Replacement: New ECM lacks the stored calibration values for the specific glow plug control module, requiring a learn procedure.
- Battery Disconnect: Extended battery power loss can erase volatile calibration data from the glow plug module’s non-volatile memory.
- Corrupted Firmware: A failed software update or corrupted flash memory inside the glow plug controller invalidates the calibration set.
- Wiring Voltage Drop: High resistance in the control or power supply circuit prevents the module from completing its self-calibration routine.
Advanced Technical Analysis
The ECM monitors the glow plug control module’s calibration status via a dedicated J1939 parameter group (PGN 65251). When the module powers up, it performs an internal self-test comparing stored reference voltages against an onboard precision resistor. If the deviation exceeds ±0.5%, the module sets an internal flag and transmits SPN 86566 FMI 13 to the ECM. This is a non-volatile fault; it remains active until a successful calibration cycle is completed.
Electrically, the glow plug controller requires a stable 12V supply within ±0.3V during the calibration window. If the supply voltage dips below 11V during engine cranking, the module may abort the calibration and log the fault. The J1939 data link must also be free of excessive noise; a corrupted CAN message can cause the ECM to misinterpret the module’s calibration status. Technicians should verify battery voltage and CAN termination resistors (120 ohms) before replacing parts.
Once SPN 86566 FMI 13 is active, the ECM defaults to a fail-safe heating strategy. It may command a fixed 2-second pre-heat regardless of coolant temperature, or in severe cases, inhibit glow plug operation entirely. This strategy protects the module from damage but increases white smoke and hydrocarbon emissions. On MAN D2676 engines, the ECM also applies a 25% torque derate until the fault is cleared and a successful calibration is confirmed via a diagnostic tool.
Long-term prevention requires performing a glow plug module calibration procedure after any ECM swap or battery disconnect. On Bosch EDC17 systems, this is done via a manufacturer-specific service routine that sends a calibration request over J1939. A real-world example: after replacing an ECM on a Mercedes-Benz OM936, the technician must run the ‘Glow Control Unit Learn’ function in Xentry. Skipping this step will cause the fault to return immediately after the first cold start, wasting diagnostic time.
Step-by-Step Troubleshooting Guide
- Verify Supply Voltage: Measure battery voltage at the glow plug module connector during cranking. Must remain above 11V DC.
- Check CAN Bus Health: Inspect CAN-H and CAN-L resistance at the module. Should be 60 ohms with bus powered off.
- Perform Calibration: Use a factory-level tool to initiate the glow plug module calibration procedure per OEM service manual.
- Clear Fault & Test: After calibration, clear the fault with the diagnostic tool. Perform a cold start cycle to verify the fault does not return.